1. Field of the Invention
The field of the invention is I/0 modules for interfacing a machine or process to a programmable controller system processor.
2. Description of the Background Art
Certain I/O modules are classified as discrete I/O modules. These I/O modules convert signals for a set of discrete I/O devices on a controlled machine or process. The operation of a discrete I/O device is associated with a single (discrete) electrical signal. This signal is generated at two different signal levels to represent the ON state and the OFF state of an input device or to control the ON state or OFF state of an output device. Typical discrete input devices are pushbuttons, limit switches and relay contacts. Typical discrete output devices are solenoids, the energizing coils in electromagnetic relays and the actuating sections of solid state relays.
The digital values for discrete I/O devices can be grouped in 8-bit groups known as "bytes" and communicated to and from a programmable controller processor during an I/O scan routine in which each I/O module is addressed in turn for I/O data transfer.
The term "word" as used in this document is a broad term encompassing data groups of four bits, eight bits, sixteen bits, two bytes or other sizes used in the computer arts, while the term "byte" refers to a word of data with a specific size of 8 bits.
The term "file" shall refer to a group of data with two or more bytes of data associated with a single starting address in memory or a single I/O address.
Another category of I/O modules known in the art of programmable controllers are word-oriented I/O modules. These require conversion of an AC or DC analog signal level to at least an 8-bit digital value and sometimes to 10-bit and 12-bit digital values. With the introduction of word-oriented modules, additional methods of I/O communication have been developed to transfer many bytes of I/O data in a single block or file between a individual I/O module and the programmable controller processor.
Struger et al., U.S. Pat. No. 4,293,924, issued Oct. 6, 1981, discloses a word-oriented I/O module that communicates multi-byte blocks or files of real time I/O data through a backplane. The module of Struger et al. was switch-selectable to operate in another mode, referred to as the single transfer mode, to alternately transfer bytes incorporating channel select data and bytes of real time I/O data. The module of Struger et al. was operable in either the block transfer mode or the single transfer mode, and was not operable in both modes during the same period of controller operation. The controller was stopped and a switch on the module was reset to change from one mode of I/O communication to the other. There was no complementary relationship between the real time I/O data communicated in one mode and the real time I/O data transmitted in the other mode. It was the same data communicated in two different ways.
More recently, in Struger et al., U.S. Pat. No. 4,691,296, issued Sept. 1, 1987, I/O modules have communicated bytes of discrete I/O data in more than one mode of operation.
The foregoing knowledge in the art, however, has not suggested automatically communicating data in a byte transfer mode and a file transfer mode to an individual I/O module. The knowledge in the art has not suggested transferring discrete I/O data indicating the ON or OFF state of the I/O devices in the first transfer mode and transferring a multibyte block or file of diagnostic data in the second transfer mode.
Word-oriented I/O modules of the type disclosed in Struger et al., U.S. Pat. No. 4,293,924, cited above, have included a programmed microprocessor and some other circuit components such as latches, which were read by the microprocessor to transfer each byte of data through the backplane during an overall communication sequence. If some method or circuit could be devised to relieve the microprocessor of this backplane communication task, the microprocessor could better concentrate on processing control tasks related to the specialized I/O circuitry linking the microprocessor to the I/O devices on the customer's machine or process.